In sewing machines equipped with one or more loopers, that is to say, chain stitch or overcase stitch machines or for so-called safety sewing machines provided with one chain stitch looper and two overcast stitch loopers, the problem arises of correct synchronization of the loopers with one another and with the corresponding needles, that is to say, the correct formation of the stitching.
Correct positioning of the loopers in respect of height is achieved in known manner with the aid of a plate which is fastened to the looper support in an adjustable manner, so that the looper is secured in the correct position. Consequently, loopers which are replaced in the course of time are always positioned against this plate in such a manner that adjustment in respect of height relative to the needles and the other loopers is achieved without the synchronization operation having to be repeated.
The same is not true of the angular position of the loopers, which in known manner is adjusted every time a looper is replaced.
The technical problem underlying the present invention is precisely that of obviating this disadvantage, in such a manner than when the loopers are replaced, they are correctly positioned without it being necessary to repeat every time the operation of angular adjustment.
This technical problem has been solved with a looper provided with a shank adapted to be fastened to its support, with the characteristic that the said looper is equipped with positioning means adapted to be coupled in a single predetermined position, onto corresponding means formed on a positioner which is mounted in the same hole of the looper support into which said looper is introduced too; distinct fastening means are provided for fixing to the support, respectively, the angularly orientable positioner and, above the latter, the shank of the looper.
More precisely, the said coupling means consists of a flat provided on the looper shank and of a similar coacting reference flat provided on the positioner.
Furthermore, the positioner, which is adapted to be inserted into a hole in the said support and is angularly orientable therein, is a cylindrical member on which the coacting flat is formed parallel to the axis of this cylindrical mamber, while similarly, the coupling flat formed on the shank of the looper is parallel to the axis of the said shank.
Finally, the aforesaid fastening means consist of two screws, of which one fastens the looper shank to the support while the other is positioned below the first screw so as to fasten only the positioner.
With such characteristics, the advantage is gained that the angular adjustment of a looper relative to the corresponding needle or to the other loopers is effected the first time and afterwards is no longer required for the other replacement loopers fitted in the course of time.